Modal Acoustic Transfer Vectors Make Acoustic Radiation Models Practical for Engines and Rotating Machinery
The paper presents Acoustic Transfer Vectors (ATVs) and Modal Acoustic Transfer Vectors (MATVs) and their use in acoustic radiation prediction, particularly from the surfaces of engines and their components and from other rotating machinery. Acoustic Transfer Vectors are input-output relations between the normal structural velocity of the radiating surface and the sound pressure at a specific point in the field. The Modal counterpart gives a similar relation, but expressed in the modal coordinates of the radiating structure. The structural response, computed with a standard FE model such as ANSYS®, can be determined either directly in the frequency domain, or (often more-efficiently) using a modal model, and this provides the boundary conditions or ‘drivers’ for the acoustic radiation. Rotating machinery applications frequently require multiple loadcases, related to different rotational speeds such as an engine run-up, as well as multiple frequencies in the acoustic response. Using ATVs or MATVs, together with interpolation techniques, the amount of heavy computations needed to produce a large volume of results in such multi-rpm/loadcase/multi-frequency problems is dramatically reduced. A speed-up factor of 100 is common, compared to conventional BEM in which each frequency has to be solved explicitly. Re-analysis with design modifications is made possible, within timescales that make the results valuable in the product development and optimisation. The computations are controlled by a new model- and solver-management environment, Virtual.LabTM, which provides an integrated tool for the functional performance analysis process, many different solution sequences using internal and external solvers, and graphical tools for creating meshes for acoustic radiation from the structural FE mesh.